Out of pure interest, I decided to do some research into what The Internet™ regarded as Steampunk Cinema. Here is a list of films that numerous sites agreed on as portraying Steampunk elements and ideals. I've ignored remakes of the same film.

Steampunk: "The term denotes works set in an era or world where steam power is still widely used. Steampunk works are usually set in the 19th century and often in Victorian era England, but incorporate prominent elements of either science fiction or fantasy, such as fictional technological inventions, or real technological developments (like the computer) occurring at an earlier date."

"Steampunk is often associated with cyberpunk and shares a similar fanbase and theme of rebellion. Apart from time period and level of technological development, the main difference between cyberpunk and steampunk is that steampunk settings usually tend to be less obviously dystopian than cyberpunk, or lack dystopian elements entirely."

I agree about Dark City not really fitting. It's placed "out of time" and, until the end where you see what's actually around the city, it can easily be said to take place in modern times, not in the past.

Maybe I'm going out on a limb here. But why not "Those Magnificent Men in Their Flying Machines" or "The Great Race." Admittedly they might be overlooked for their whacky content. But in "TMMITFM" they come up with some outrageous contraptions and in "TGR," Dr. Fate's car more than qualifies it for consideration.

Love steampunk, though its exact meaning is up for debate.
Some suggestions:
"The Golden Compass"
"Hugo"
"The Fabulous World of Jules Verne"
"City of Ember"
"A Trip to the Moon" (many of Georges Melies' films could be considered steampunk, but this is his most famous and one of his best)
"Mysterious Island"